Several systems for providing emergency light in case of failure of the local electricity supply have been developed. For example, U.S. Pat. No. 5,426,347 discloses an arrangement consisting of a power supply for providing a high frequency current, a lamp holder including a lamp socket, and a fluorescent lamp capable of being screwed into the socket. An alternate embodiment of this Patent includes a rechargeable battery and appropriate circuitry to allow the operation of the lamp in the case of failure of the power line voltage. As another example, U.S. Pat. No. 5,473,517 discloses an emergency light that is electrically and mechanically connected to a conventional light switch. The unit contains a power-interruption detector connected to a relay that supplies DC power from self contained batteries to power a 5, 7, or 9 watt fluorescent lamp or an incandescent lamp as an emergency light source. However, none of the conventional illumination units have the capability of supplying light with the unit's lamp on demand, under normal conditions when provided with AC power supplied by the electricity network and of automatically continuing to supply light by the same lamp, if still demanded, when a power failure occurs. Nor, conversely, do they have the capability of supplying light with the unit's lamp on demand, when a power failure occurs, and of automatically continuing to supply light by the same lamp, if still demanded, under normal conditions, when provided with AC power supplied by the electricity network. Furthermore, the conventional illumination units function as an additional lighting source to other common existing light sources, and therefore they usually needs additional means for placing them on walls or ceiling.
It is therefore an object of the present invention to provide an illumination unit, having on demand illumination capability during both normal and emergency conditions.
It is another object of the present invention to provide an illumination unit which is capable of automatically detecting a demand for illumination and in response, of providing such illumination under any condition.
It is still an object of the present invention to provide an illumination unit capable of being placed in an existing light source housing.
Further purposes and advantages of this invention will appear as the description proceeds.